Parity among the field will explode as an issue if McLaughlin, already the reigning champion, extends his series lead at the Grand Prix.

The Kiwi star was untouchable at the Adelaide 500, winning both races in style. Mostert looks the likeliest bet to challenge the New Zealanders on the evidence of practice - despite his man-flu.

"I've had it since Adelaide. I'm losing my voice and got those hot feels on," he said.

"Once you're in (the car) it's fine."

Shane van Gisbergen endured a tough day, battling a torrid splitter vibration to finish well down the order in both sessions.

The Supercars field will race for championship points and the Larry Perkins Trophy in Melbourne, competing over four races between Friday and Sunday. Qualifying for the first two races takes place later on Thursday afternoon.

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